Note: Descriptions are shown in the official language in which they were submitted.
%~
- 1 -
"SYNTHETIC D0
, Field of the_lnvention
The invention relates to a synthetic thermal insulator
made of fibrous components and more particularly relates to
such a material which is a replacement for down.
. .
srief Descri t_on of the Prior Art
Representative of the prior art are disclosures given
in the U.S. Patents 3,892,909; 4,042,740; 4,118,531, 6
4,134,167; 4,167,604; 4,364,996; 4,418,103; and U.
Application 2,050,818A.
The superiority of down as a lightweight clothing and
bedding insulator has been recognized for centuries. In
spite of several recent and very worthwhile advances in
synthetic insulation, down has retained its status as the
ultimate, lightweight insulator. Its insulating e~ficiency
has not yet ~een equalled by a commercially-a~ailable product
with the minimal density of a typical down filling. The
loftiness that characterizes down and makes it such an e~fi-
cient thermal barrier is unique in a further sense; it is
recovered almost completely when a compressed down assembly
' ` '
,
.
80~ 30
is aqitated. The loft-related virtues of down e~ist only
under dry conditions, however, and loss of loft and an accom-
panving deterioration in thermal performance when wet is the
primary shortcoming of down in field applications.
We have discovered that a very particular blend of micro-
fibers and macrofibers produces a synthetic alternative to
down. The blend of the invention compares favorably to down
or mixtures of down with .eathers as an insulator in that it
will:
a. Provide an equally efficient thermal barrier,
b. Be of equivalent density,
c. Possess similar compressional properties,
d. Have improved wetting and dr~ing characteristics,
and
e. Have superior loft retention while wet.
Background information relating to some of these performance
characteristics is given ~elow.
Down sleepin~ bags and garments are extremely efficient
th`ermal insulators because they have a very low internal heat
transfer coefficient at all ~ulk densities when compared to
the alternative materials presently employed. Moreover,
e~perimental data also shows that the relative advantage of
down becomes greater at the very'low bulk densities at which
it is generally used. In the literature it is common prac-
tice to compare the thermal performance of materials in terms
of an 'apparent or effective thermal conductivity'. However
..
~28013~
it is e~trPmely important to realize that for fibrous insula-
ting materials at the bulk densities that are of interest in
personal cold-weather protection applications, the heat trans-
fer is as much due to radiation and convection as it is to
conduction in the fibers and the air. Consequently, improve-
ments (decreases) in heat transfer by any of the three
mechanisms of conduction, radiation and convection can
potentially lead to performance improvements, and the present
invention pays particular attention to the radiation companent
of the heat transfer, and takes advantage-of a previously
unappreciated characteristic of radiative transer.
In practice the balance between the three heat transport
modes depends on the test or usage conditions as well as the
sample st~ucture and con~iguration. For instance, when we
measure the 'apparent' thermal conductivities of various
webs at a certain temperature gradient and mean temperature
( a T = 50F, tm = 75F were selected as standard in our
case) we have to remember that the results depend on the
direction of heat flow. It is known that heat 1OW 'down'
tests eliminate convection, so most samples were evaluated
in this con~iguration. This simpli~ies the intexpretation
of the e~perimental data since only two modes of heat
transfer, namely conductlon and radiation are operative, and
moreover since the conductive component is readily
calculable ~or assemblies o these densities the critical
role o~ radiation is easy to demonstrate.
. ~, . .
. .
`` ~2~3013~0
-- 4 --
Heat transfer ~y thermal conduction in a low density
fibrous weh occurs by conduction across the air gaps and by
conduction through and between fibers. The conduction can
be treated theoretically as takinq place in a two-phase
mixture of air and fibers - the air beinq the matrix and the
fibers the included component. The standard mixture laws
for two-phase systems apply and the overall conductivity kC
is given by
C ftXa~kf,VF)
where ka and kf are the conductivities of the air and solid
fiber and VF is the volume fraction of fiber in the web
assembly, such that
V~ = PF~Pf~
and PF and P~ are the web and fiber material densities.
The form of the appropriate mixture law depends upon the
geometry of the system and many attempts have been made to de-
rive generalized representations of the functionality expressed
by the expression of KC above. Examination of these results
shows that the general orm for low density assemblies is
~ ~ k
where ~ is a function o~ the geometry and ka c r c kf.
When VF is very small ( ~ 0.01), then a good approximation
~within 23) is simply
kC ~ k
and this approximation is qenerally adequate over the ran~e
of densities -that is of interest in the applications consi-
dered here. ~hus it is possible to conclude that the heat
." .
. .
~ ~2Bo~a~
-- 5 --
trans~er bv conduction is essentially controlled by the con-
ductivity of air, ka~ and this can not be reduced unless some
form of evacuated svstem is used. Hence in order to reduce
the heat transfer it is necessary to manipulate the radiation
and natural convection conductivities. Since the test method-
ology used is such that the convective co~ponen~ is s~ppressed,
it is sufficient to focus attention on the radiative component.
We have seen that if the only (or the main~ heat trans-
fer mechanism in low density fiber batts or webs was by heat
conduction, we would expect the 'conductivity' to be constant
- or to increase slightly with increased density This is
not found to be the case, however, as shown by the experimen-
tal data o~ Finc~ ], Baxter[ ], Fournier and Klarsfeld[ ],
and Farnworth~4] for various materials and by Rees[51 for
down. In fact, if the 'conductivity' is measured for the
same material over a range of decreasing densities, it is seen
that the conductivity decreases to a minimum and then the con-
ductivity increases as density decreases, at a faster and
faster rate.
[1] Finck, J.L., "Mechanisms o~ Heat Flow in Fi~rous
Materials", J.N.B.S., 1930
~2] Baxter, S., "The Thermal Conductivity of Te~tiles",
Proc. Physics Soc., 1946
~3] Fournier, D. and Xlars~eld, S., "Some Recent
Experimental Data on Glass Fiber Insulting Materials,
etc.", AST~ STP 544, 1974
[4] Farnworth, ~., "Mechanisms o~ Heat Flow Through
Clothing Insulation", TRJ, 12, 1983
[5] Rees, W.M., Shirley Institute Con~erence on Comfort,
1978
~280~80
-- 6 --
The large conductivity at low densities is due to radiation
if the heat flow direction is downwards or to radiation and
natural convection when the heat flow direction is upwards.
E~perimental data for down at a ranqe of de~sities measured
with the heat flow down is shown in Fiqure 1, and since there
is no convective component the increase in heat transfer at
low densities is clearly attributable to radiation. The
direct plot of effective thermal conductivity as a function
of density PF does not permit ready comparisons between
materials since it is not easy to estimate relevant charac-
terizing parameters from a curvilinear plot. However, it is
found that a plot of the product ~PF against PF for low
densitv fiber assemblies gives a straight line with a slope
equal to the conductivity of air, ka, and the intercept o~
this plot on the kPF axis permits a quantification of the
radiative heat transfer. This intercept, C, with units o
~stu in/hr ft2 F) (lb/ft3) in the British system is called
the radiation parameter, and in order to produce the lowest
possible heat transfer through a fiber assembly, this radia-
tive parameter should be reduced to its minimum value~
Table I gives measured values of this parameter for a
wide range of polymeric ~iber assemblies, together with
details of the test materials, and ~igure ~ shows a plot o~
the radiation parameter against fiber diameter The general
tendency that is clear from t~e experimental results is that
the radiative parameter is reduced as the fiber diameter is
decreased, with the result that the e~fective thermal resis-
- - -
;
'~. :
`- ~2t3~118~0
-- 7 --
tance of the assembly is increased. It is eaually clear,
however, that this reduction in fiber diameter is not benefi-
cial without limit, since the samples of fiber assemblies
containing microfibers show a sharp increase in radiation
parameter. One of these assemblies is a commercial manifes-
tation of the material described by ~auser tU.S. Patent
4,118,531) and Hauser's unequivocal statement ~col. 4, line
24~ that "The finer the microfibers in a web of the invention
the better the thermal resistance" is demonstrably untrue.
It is interesting and significant that down, in which the
fine fiber component has a diameter ranqe of 2.5 to 11.0
microns, appears to be situated at the minimum of the curve
relating the radiation parameter to fiber diameter, and any
synthetic polymeric fiber assembly attemptinq to emulate the
thermal properties of down must also be so situated. One of
the surprising and -novel aspects of the present invention is
that it is demonstrated that this will not be p~ssible if
the fiber assembly contains a si~nificant proportion of very
fine fibers (here deEined as having diameters smaller than 3
microns), and since the slope of the curve is extremely steep
on the small diameter side of the minimum, then only a small
fraction of very fine fiber is sufficient to compromise the
low value of the radiation parameter. In order to maintain
a minimal value of the radiation parameter it is desirahle
that the fiber assembly contain no more than 5~ of fiber
material with a diameter smaller than 3 microns.
.
~ 8 --
TA~LE I
Values or the Radi2tion Par2~e~er C
Radiation Par~e~_,C
~nsit~~ Dia~ete- ~tu- n_ x lb x 10
P ~enier d(u) hr rt~ ~F ft3
f
~n 1~30 - ~.5-ll.0 4.8
A~ny Res. Co. PEr 1.38 0.5 . 7., 4.2
Teijin PET 1~38 0.8 10 5.2
B ~nt D102 PEr 1.38 1.6 13 7.0
~elanese Polaryuard PET 1.38 S 23 lO.1
~ollofil 808 PET 1.17 S.S 26 11.8
~ollofil II PET 1.17 S.S 26 11.4
~ollofil 91 PET 1.17 15 42 14.5
~elt-blown pol olef~n 0.90 -- 1-3 9.4
Melt-~lown DEr 1.38 - 1-3 8.1
Hollor~ O= ~=.OS) 1.17 5.5 26 8.7
Ke~lar 49 1.4 1.~ 12 8.4
Black PET 1.38 4.5 21 13.0
: Examination of Figure 2 allows reasonable estimates of
the upper le~els or fiber diameter permissible if t~e thermal
properties of the assembly are to be maintained. r~ we set
a limit of 0.075 units (atu in/hr ft2 F) llb/ft" for the
radiation parameter, then the plot indicates ~hat the ~ulk
of the fibers must lie within the diameter range of 3.0 to
12.0 microns and measurement of the thermal conductivi~y of
a n~nber of webs confirms this conclusion.
T~3Je /~r/<
''''
. ~ :
~ ~2~301~30
g
The discussion p,esented above dealt with the physical
parameters that control the thermal properties of low-density
fiber assemblies; in order to produce a satisfactory down sub-
stitute material it is necessary also to examine the mecha-
nical behavior or such an assembly, and attempt to determine
the optimum configuration for the assembly. This relates not
onlv to the ability o' the assembly to maintain its preferred
geometrical form but also gives some indication of the deqree
of dif'iculty that might be encountered in establishing the
assembly during the manufacturing process. Measurements of
the thermal behavior indicate`that improved performance is
generallv associated with small diameter fibers, bu~ that
; there is a lower limit of about 3 microns below whic~ the
thermal performance begins to deteriorate significantly.
From a mechanical standpoint it is a matter of experience
that e~ctremely fine fibers suffer from deficiencies or ri-
giditv and strength that make them dificult to produce,
manipulate and use, and there is thererore a minimum fiber
diameter below which efforts to realize improved perfor~ance
are not worthwhile. It is generally ac~nowledged that very
fine fibers produce assemblies that exhibit very poor reco-
very from compressive deformation. All the currently-avail-
able commercial webs made from microdenier fibers exist only
as dense structures, since they fall within ~he practical
limits set by the fiber rigidity and are continuously sub-
jected to consolidating forces throughout their use-life.
rt is interesting that this behavior is in marked contrast
,',
- ~28C~ 0
- 10 - -
to that of down, which is renowned for the renewable nature
of its loft. It is likely that the unusual behavior of the
down is related primarily to the svstem of nodes that exist
on the ribrillae, which lead to a predisposition of a low
density confi~uration under certain circumstances. The re-
covery behavior is probably also aided by the presence of
the small fraction of large diameter, stiffer filamentary
material in the down assembly. Whatever the reason for the
lofting potential of down, the maintenance of a low density
is extremely important to the concept of lightweight warmth
and is an essential feature of any viable down substitute
material.
The problems associated with the mechanical stability
of fine fiber assemblies are exacerbated in the wet condition
since the sur~ace tension forces associated with the presence
of capillary water are considerably greater than those due to
gravitational forces or other normal use loading and they
have a much more deleterious effect on the str~cture~ A
simple calculation suggests that the residual deformation in
a wet assembly is likely to be at least one order of maqni-
tude more severe than for a dry assembly due to gravitational
loadin~ even under the best conditions. T~is calculation il-
lustrates dramatically the extreme vulnerability to collapse
of fine fibrous assemblies under capillary forces. ~oreaver
the estimate unquestionably underestimates the situation since
the Young's modulus of polymeric materials can typically be
reduced by at least one order of magnitude when wet, which
... . . .. . . ........... ..
. ~ .
~L2~3C18~30
will further increase the seriousness of the effect. Under
wet conditions, anal~sis suggests that an assembly made of
filaments with diameters below 10 microns could be e~tremely
vulnerable to collapse under saturating condi-tions and expe-
rimental evidence fully confirms this expectation both for
down and for synthetic polymer assemblies. It is hiqhly
desirable to have the filaments mzde from a polymer such as
polyester, polyolefin or polyaramid whose mechanical proper-
ties are not significantly reduced on wetting. Even if the
polymer itself is insensitive to the effects of moisture it
is also important to treat the fibers with a water-repellant
finish. The down of commerce is usually treated in this way,
and all th~ experimental data on down presented herein is for
down so treated; similarly the synthetic polymer insulator
materials described of this invention also require water
repellant treatments to realize their full insulating and
mechanical potential in the wet state.
The mechanical limitations of fine fiber assemblies
discussed above present a serious conflict in light of the
fiber diameters needed for improved thermal performance.
The range of requ1rements, both thermal and mechanical, that
the down substitute must fulfill ma~e it almost inevitable
that the assembly be made up from fibers of more than one
diameter class: the small diameter fibers being responsible
for the thermal performance o_ the assembly, with their dia-
meter alling within the range that was discussed in the
previous paragraph, namely between 3 microns and 12 microns,
, . .. . .
~z~o~o
- 12 -
and the large diameter fibers beinq responsible for the me-
chanical per~ormance of the assembly. Just as there are
limits to the diameter range of the smaller active diameter
component of the blend, so there are reasonable limits that
can be set on the large diameter component. We consider
first the length ~f of filament of denier 3 t~at is con-
tained in a unit cube of assembly of volume fraction VF and
can show that an assembly of O.Ol volume fraction made up
entirelv of l denier fibers contains approximately 104 cm of
fiber. This is given by:
~ f = 9 x lO PfVF/D,
and this e~pression demonstrates that if we attempt to
improve the mechanical per~ormance of the assembly by the
addition of large diameter fibers, we obviously have avail-
able a shorter length of material: for example the addition
of lO~ of 100 denier fiber involves only a lO centimeter
length of material. In order to be effective, this length
of fiber must be distributed uniformly within the l cm cube
in a configuration that permits goad recovery from compres-
sive loading in any direction, and such a distribution is
essentially impossible to attain. Calculation indicates
that the ma~imum fiber diameter that can be tolerated~as a
recovery modifier in a low density assembly is approximately
30 denier, and smaller denier materials would be preferred
for minimum impact on the volume fraction.
....... ... . . ..... . ...... . . ... ... . . ... . . . .. .. . ..
- 13 -
The foregoing discussion addresses the issue of how much
additional high denier material can be tolerated: it is
equally important to attempt to estimate how much is needed.
The mechanism of deformation of the high-denier component will
be principally bending and torsion, and in each of these modes
of deformation the flexural riqidity of a circular filament
varies as the fourth power of the diameter, and the stiffness
of a fle~ural or torsional beam varies inversely as the third
power of the length of the element. The deformation stiffness
S of the assembly can be written
S dC EI/~ 3
where ~ is the free length of fi~er between contact points.
Since I dC d4 and ~ oC d/VF it is possible to write:
S co dVF3 '
This expression shows the e~treme sensitivity of t~e stiffness
of the assembly to the volume fraction, and the relative in-
sensitivity to the fiber diameter, since the geometrical
parameters of the assembly geometry offset the large changes
in filament properties. This suggests that the use of high
denier fibers is particularly valuable in very low density
assemblies. The combined analysis suggests that the larger
fiber in a low density mi~ed assembly should ideally have a
diameter of approximately S0 microns in order to ma~imize
the mechanical performance at a given density, and that a
l0~ weight of mixture should be adequate.
~SUMMARY OF THE INVENTION
The invention comprises a thermal insulation material,
~hich comprise~ a blend of
..... . . . : . ~ . . .
280a~[)
14 -
(a) 80 to 95 weight percent of spun and drawn, crimpedf
staple, synthetic polymeric microfibers having a
diameter of from 3 to 12 microns; and
Ib) 5 to 20 weight percent of synthetic polymeric
staple macrofibers having a diameter of from more
than 12, up to 50 microns.
The insulation material of the invention is useful as a
replacement for down and down/feather mixtures in clothing,
bedding and like articles of insulation.
BRIEF DESCRIPTION OF THE DRAWINGS
Figure 1 is a graph plotting the effective thermal
conductivity as a function of density for down insulation.
Figure 2 is a graphical representation plotting the
radiation parameter against fiber diameter for a number of
different fibers.
DETAILED DESCRIPT~ON OF ~HE PREFERRED
: EMBODIMENTS OF ~HE INVENTION
The thermal insulation material of the invention com-
prises a blend of two different textile fibers. The fibers
differ, essentially, in their diameters. The majority of the
fibers in the blend are microfibers, with a diameter within
the range of from 3 to 12 microns. The minor proportion of
the blend is made up with macrofibers, i.e., fibers having a
di~meter o more t~an lZ mic on~ p ~ abou~ ~ c ons
,, , ~
128C)B80
- 15
The microfibers employed in preparinq the bLended mate-
rials of the preferred form of the invention are spun and
drawn micro~ibers o~ a polyester, pre~erably oE polyethylene
terephthalate, though other polymeric materials ma~ also be
used in this invention. Methods of their manufacture are
well known; see for example U.S. Patent 4,148,103. Advanta-
geously the microfibers are drawn following their ex~rusion,
to achieve a high tensile modulus, which is about 70 to 90
gms/denier ln the present example. A relatively high tensile
modulus contributes to a high bending modulus in the material
of the invention, and helps with the mechanical performance.
Advantaqeouslyt the macrofi~ers are also spun and drawn
fi~:ers of a synthetic polymeric resln such as a polyester
(preferably polyethylene terephthalate). We have also found
macrofibers of polyaramids such as poly(p-phenylene tereph-
thalamide) to be advantageous. Macrofibers of poly(p-
~ ' ~
phenylene terephthalamine) are commercially available underthe trademark Kevlar.
,l~` The microfibers and preferably the macrofibers making
~, I
'~ up the thermally insulative blends of the invention are
~; crimped fibers slnce this makes it possible to produce low
i density intimate blends of the two components. The tech-
j~ niques for crimping fibers are well known and process details
,¦ need not be recited here. Advantageously the average crimp
`' i number for both the microfibers and the macrofibers is within
the range of from 8 to 20 crimps per inch. It is possible
i to achieve satisfactory results with uncrimped macrofibers
:~ :
. ,
~` -,
,
..... ~ . .. . .. . . .. , . .. ~ , ,, , ~ , ... ...
,
`
'` ~ :
8(~ 80
- 16 -
but I believe that the presence o~' crimp on the micro~ibercomponent is critical to the success~ul operation o~ a low
density, lofty assembly. The pre~ence of individualized
opened and crimped microfiber also helps to make it possible
to reestablish loft in the fiber assembly after compression
or wetting, and hence improve the long term utility o~ the
invention.
The microfibers and the macrofibers employed in the
blends of the invention may, optionally, be lubricated.
Representative of lubricants conventionally used are aqueous
solutlons of organopolysiloxanes, emulsions of polytetra-
fluoroethylene, non-ionic surfactants and the like. Such
lubricants may be applied to the fibers by spray or dip
techniques we}l known in the art.
The macrofibers and the microflbers are blended toqether
to form batts consisting of plied card-laps, although other
fibrous forms may be equally suitable. The card laps, or out-
put webs from a carding machine, are intimate blends of spun-
and-drawn microfibers~and macrofibers.; The batts are adYan-
tageously made to achieve densities comparable to the densi-
ties characteristic of down, i.e., on the order of less than
1.0 Ib/cubic oot, tvpically around 0.5 lb/cubic foot.
The follow1nq examples describe the manner and process
~1 ~ of making and using the invention and set forth the best mode
contemplated by the inventor for carrying out the invention
but are not to be construed as limiting. ~here reported,
the following tests were employed:
.
:;.. , ~. :
- : :
,- ~ .
:.
~2 !3~)~8~)
- 17 -
Densitv The volume o~ each insulator sample was
determined by ~ixing two plana~ 9ample
dimensions and then measuring thickness at
0.002 lb/in. 2 pressure. The mass of each
sample divided by the volume thus obtained is
the basis for densitv values reported herein.
¦ Th~ckness was measured at 0.002 lb/in.1.
AD~arent thermal conductiv tv was measured in accord
~ith the p}ate/sample/plate method described
by ASTM Method C518.
~ : :
Compressional Strain Strain at 5 lbJin.', which was the
~; maximum strain in the compressional recovery
test sequence, was recorded for each test.
Compressional Recovery and Work of ComDression and
Recovery Secti~on 4.3.2 o Mllitary Specific-
ation MIL-B-41826E describes a compressional-
recovery test technique for fibrous batting
that was~adapted for this work. The essential
; di'~erence between the Military Speci'ication
method and the one employed is the lower
pres~sure at which 1nitial~th1ckness and
recovered-to-thic~ness~were measured. The
,
;l ~ measuring pressure inlthe speci-ication is
: ~ ~
~ ~ 0.01 lb/~in~', whereas 0.002 lb/in~' was used
:
~ ~ ~ in this work.
~: :
:
. :
.,
. ~: `- ` :
: '
:
.. : ,
~8088
18 -
Water Absorption Capacity AS~M Method D1117 provided
the starting point for development o~ the
water absorption- capacLty and absorption-
time test used. However, wetted- sample
weighinss were made at frequent intervals
during the first six,hours o~ immersion and
another weighing was made after twenty-Four
hours ~Method D11l7 requires only one wetted~
samp1e weighing). A unique sample-holder and
a repeatable technique for draining excess
water prior to each weighing were adopted
after some in~tial experimentation.
:
~ ~ Dryin~ Time After each absorption capacity test,
:
weighings w re made at one-half hour
intervals as the~sample air-dried on a wire
rack in a 70F., 65~ r.h. atmosphere.
The down used throughout t~e examples was actually a
down/fea-hers mixture,~80t20 by weight, per MIL F-43097G,
Type II, Class I. ~his mixture is commonly and commercially
referred to as "down" and is~often~re erred to as "down"
: hereln.
Example 1
A quantity of spun~and drawn l.2 inch long microfibers
I having a diameter of 7.5 microns is provided. The fibe~ are
lubricated w1th a silicone finish. The spun-and-drawn micro-
fibers are polyester~and have been drawn to achieve a rela-
:
-'
:
~; : ,. ... .
.:
~- . ` . ~
,
~2RO~F30
19
tively high tensile modulus ~60-90 grams/denier), which
co~tributes significantly to a high bending modulus. A~te~
drawing they have been crimped, cut into staple and thoroughly
opened, or separated, in~a card. The high bending stiffness
and crimp are essential characteristics which provide and
help to maintain advantageous loft. The average crimp fre-
quency is 14/inch and the average crimp amplitude is 0.04
inches. Loft and compressional characteristics are improved
further through the blending wlth 10 percent by weight of
macrofibers of the ~ame polyester ~polyethylene terephthalate)
having diameters of 25.5 microns. The macrofihers are
lubricated with a silicone finish and are characterized in
part by a staple length of 2.2 inches, an average crimp
frequency of 8.5linch and a crimp ampiitude (average) of
0.06 inches. The blend is carded into a batt. The physical
properties of the batt are shown in Table II, below,
compared to a batt of down.
:::
~:
: : : :
: .: ~:
Example 2
; ~ ~The procedure of Example 1, supra., is repeated except
that the macrolber as used thereln 5 replaced with 20
percent by weight of uncrimped poly(p-phenylene terephthala-
mide) fibers having a diameter of 12 microns, a length of
:
3.0 inches, and a silicone lubricant finish. The physical
:
! ~ characteristics of the material formed are given in Table II
below.
: ~
:
....
.~ . ...... ~ . ... . . . . . . ... . . .. . .
.
.
~2B08~30
- 20 -
TABLE II
____
Apparent thermal co~ductivity 0.180 0.281 0.271
(Btu-in./hr-~t2-F)
m erm~l cond. test density (lb/Et3)0.45 0.47 0.48
Minimum density (lb/ft') 0.24 0.25 ~.25
Comp. strain at S Ib/in.l~3)b 95 96 92
Comp. reoovery from 5 Lb/in.~(~)b 102 112 112
Work to compress to S lb/in.a 4.91 3.49 3.57
(~in.l
ResilienceC 0.53 0.62 0.60
Wettinq during Immersi n
.
Water ~ sorption after 20 min. 1.16 2.16 1.41
Density after 20 mQn wetting 0.48 0.50 O.S1
wetting (Ib/ft~) -
Water absorption after 6 hr ~x dw)3.75 5.15 3.44
l :
'~ Density after 6 hr wetting llbi~t')3.55 0.94 1.02
. 1 .
Drvin~ after 24 hrs. Water Im~ersion
~ ',~ ght after 30 min drying (x dw)3.88 4.83 3.29
j ~ Density aft~r 30 min drying (lb~ft3) 5.2lJ 0.95 0.90
Weight after 6 hr~drving (x dw) 2.45 1.68 l.Oi
Density after 6 hr drying (Ib~ft3)3.20 0.41 0.44
~j :
I ~ a. Heat flow down. 2.06 in~ specimen thickness.
b. Gauge l~ gth: 2.00 inches: density at 2.00 inch thickness was 0.50 Ib/ft3.
c. Resilience equals: work-o~-recovery divided bv work-to-compre
d. x dw: times dry-weight
, : ' .
.'
, . . ... . . . .. . ... .. . ..
,
: ; ;
~,
8~ 0
- 21 ~
It can be seem from the above Table II that, in most
instances, both examples of the invention offer per~ormance
equivalent to that o~ the down/feathers mixture, and that
the values of compressional recovery, work to compress, and
resilience measured for both embodiments represent some
improvement over those of down. Improvement of perhaps
greater significance is apparent through comparison of
densities at the "6 hr wetting," "30 min drying" and "6 hr
drying" intervals in the wetting/drying cycle. The much
lower densities measured for the two forms of the invention
show ~hat it retains its loft while wet and, most probably
its lnsulating value, to a far greater degree than does
down. Resistance-to-wetting and resistance to loss-of-loft
while wet are inherent advantages of the fiber combination
described. The hydrophobic nature of polyester and the
1:
¦ microporous structure of the insulators are assumed to
contribute to these desirable characteristics.
;~
1 :
', , :
